The invention relates generally to metal oxide ceramic films used in integrated circuits (ICs). More particularly, the invention relates to reducing or counteracting degradation of the metal oxide ceramic due to excessive loss of a mobile specie from the film.
Metal oxide ceramic materials have been investigated for their use in ICs. For example, metal oxide ceramics that are ferroelectrics or are capable of being transformed into ferroelectrics are useful due to their high remanant polarization (2Pr) and reliable long-term storage characteristics.
Various techniques, such as sol-gel, chemical vapor deposition (CVD), sputtering, or pulsed laser deposition (PLD), have been developed for depositing ferroelectric films on a substrate. Such techniques, for example, are described, for example, Budd et al., Brit. Ceram. Soc. Proc., 36, p107 (1985); Brierley et al., Ferroelectrics, 91, p181 (1989), Takayama et al., J. Appl. Phys., 65, p1666 (1989); Morimoto et al., J. Jap. Appl. Phys. 318, 9296 (1992); and co-pending United States Patent Applications U.S. Ser. No. 08/975,087, titled xe2x80x9cLow Temperature CVD Process using B-Diketonate Bismuth Precursor for the Preparation of Bismuth Ceramic Thin Films for Integration into Ferroelectric Memory Devices,xe2x80x9d U.S. Ser. No. 09/107,861, titled xe2x80x9cAmorphously Deposited Metal Oxide Ceramic Films,xe2x80x9d all of which are herein incorporated by reference for all purposes.
Metal oxide ceramics are often treated with a post-deposition thermal process at a relatively high temperature in order to produce resulting materials with the desired electrical characteristics. For example, some Bi-based oxide ceramics such as strontium bismuth tantalate (SBT) are thermally treated by a xe2x80x9cferroanneal.xe2x80x9d The ferroanneal converts the as-deposited films into the ferroelectric phase. After the as-deposited films are converted into the ferroelectric phase, the ferroanneal continues, growing the grain size (e.g., greater than about 180 nm) of the films in order to achieve a good remanent polarization. Other types of metal oxide ceramics can be deposited as ferroelectrics. For example, lead zirconium titanate (PZT) is often deposited at a relatively higher temperature, such as greater than 500xc2x0 C., to form an as-deposited film with a ferroelectric perovskite phase. Although the PZT is deposited as a ferroelectric, a post-deposition thermal process is often still needed to improve its electrical characteristics.
Typically, the metal oxide ceramics comprise a mobile specie. The high temperature of the post-deposition heat treatment causes diffusion of the mobile specie out of the metal oxide ceramic layer. The amount of mobile specie that diffuses out of the metal oxide ceramic layer is referred to as an xe2x80x9cexcess mobile specie.xe2x80x9d The mobile specie can be in the form of atoms, molecules, or compounds. Diffusion of the excess mobile specie can result in a metal oxide ceramic having an incorrect stoichiometry. This can have a detrimental effect on the electrical properties, such as remanent polarization (2Pr) and leakage current, because they depend highly on the material composition.
Additionally, the diffusion of the excess mobile specie can have an adverse impact on yields. The excess mobile specie can easily migrate through the bottom electrode and into other regions of the IC during the post deposition heat treatment, which can cause shorts and/or alter the electrical properties of other device regions such as the diffusion regions.
As evidenced by the foregoing discussion, it is desirable to counteract the adverse effects caused by diffusion of an excess mobile specie from a metal oxide ceramic layer.
The invention relates to metal oxide ceramic films and their applications in ICs. More particularly, the invention relates to reducing the degradation of metal oxide ceramic due to the diffusion of an excess mobile specie.
In accordance with one aspect of the invention, degradation of the metal oxide ceramic due to diffusion of the mobile specie is reduced. In one embodiment, a compensation layer is provided beneath the metal oxide ceramic. The compensation layer comprises the mobile specie to compensate the metal oxide ceramic for the loss of the excess mobile specie due to diffusion during the post-deposition heat treatment. The mobile specie from the compensation layer migrates to the metal oxide ceramic, replenishing it with the mobile specie to ensure that the metal oxide comprises the correct or desired stoichiometry to achieve good electrical properties.
In another embodiment, the compensation layer comprises a material that facilitates the formation of the desired phase in the metal oxide ceramic layer during the post-deposition heat treatment. Forming the desired phase in the metal oxide ceramic reduces the degradation of the metal oxide ceramic due to diffusion of the mobile specie. In one embodiment, the compensation layer facilitates the formation of a ferroelectric phase in the metal oxide ceramic layer during the post-deposition heat treatment.
In yet another embodiment, the stoichiometry or composition of the metal oxide ceramic is selected to reduce or minimize diffusion of the mobile specie without adversely affecting the electrical properties of the material. Additionally, the deposition parameters of the metal oxide ceramic can be controlled to reduce the diffusion of the excess mobile specie from the metal oxide ceramic. In one embodiment, the ratio of oxidizer to the precursor is reduced to reduce diffusion of the mobile specie.
In another aspect of the invention, diffusion of the excess mobile specie through the bottom electrode and into the substrate below is reduced. In one embodiment a barrier layer is provided below the metal oxide ceramic. The barrier layer reacts with the mobile specie during the post deposition heat treatment. The reaction consumes the mobile specie, preventing it from diffusing through the electrode. The barrier layer can also serve as a compensation layer to facilitate formation of the desired phase in the metal oxide ceramic.
In another embodiment, the diffusion pathway along the grain boundaries of the conductive layer on which the metal oxide ceramic is formed (e.g., bottom electrode) is blocked to reduce the diffusion of the mobile specie into unwanted regions of the device. In one embodiment, the conductive layer comprises a material that oxidizes during the post-deposition heat treatment. The formed oxide either segregates from the conductive material and fills the gaps between grain boundaries of the electrode or is integrated with the conductive material to change the chemical nature of the metal oxide ceramic/conductive layer interface to prevent the mobile specie from diffusing through. Preferably, the oxide molecules react with the mobile specie to trap it in the conductive layer. The conductive material can also prevent the migration of oxygen into unwanted regions of the device.